Treatment of wood



Patented Nov. 17, 1942 Julius F. T.

Wilmington, DeL, asslgnors to E.

Berliner and Hemline M. Kvalncs,

I. do lPont de Nemours & Company, Wilmington, Del., a. corporation of Delaware Application August 22, 1940, Serial No. 353,696

No Drawing.

, 6 Ciaims.

This invention relates to the treatment of wood and more particularly to the chemical seasoning of wood.

In the lumber industry, one of the most serious problems has been that of checking and cracking of wood during its storage and drying after cutting of the timber. This checking and cracking of,woo d is due, primarily, to the shrinkage resulting from drying of the outer area or portions of green wood at a more rapid rate than the interior portions.- As a consequence of this uneven shrinkage, surface strains and stresses are set up which cause extensive cracking, checking or splitting of the green lumber, being most apparent at the ends and along the surface of the lumber in the central portions of the flat grain cuts.

Various'proposals have been'made to overcome these problems but heretofore none have proven commercially practicable.

It is an object of this invention to overcome the drying problem in the lumber industry and to provide a new and improved method for treatmg or.seasoning lumber.

Other objects and advantages of this invention will be apparent from the following specification inwhichits preferred embodiments and details are described.

We have found that the checking and crack ing of wood may be greatly reduced by treating wood with a urea solution of such concentration, at the particular temperature employedthat at the wood surface the urea solution is completely saturated; 'Preferably the wood temperature is at a-temperature in the range of to 15 C. below i the temperature of the urea solution, and. the

urea solution is saturated at the temperature at which it is utilized.

The process of this invention is applicable to wood generally, whether unseasoned or partiy seasoned or, in fact, if the wood contains any moisture which it is desired. to remove. Thus,

for example, the water content or green wood,

based upon the dry weight of the wood, may vary from about 30 to 266% or more. Such unis reduced by treatment with urea, followed by air or kiln drying of the urea-treated wood.

The amount of urea absorbed on the wood surface by the process of this invention is increased greatly over what would be expected, based upon the urea concentration. Upon removal of wood from the saturated urea solution a mat of urea in the form of a fine, intertwined, closely adher ing precipitate of crystalline urea is formed upon the surface of the wood encasing relatively large amounts of urea solution contiguous to the wood.

surface. A The crystallized urea mat adheres so strongly to the wood that it is not readily removed by brushing or chipping from rough cut lumber. This mat of urea subsequently dissolves in the water content of the wood, thus further impregnating the wood surfaces.

Although the dipping of the wood may vary over a wide time interval we have found that about 5 to30 seconds treatment is highly effective, with a period of 10 to 15 seconds being the preferred time intervaL- r By the process of this invention, wood surfaces are maintained'pervious to the passage of mois-.

ture from within the wood so that the interior moisture may continuo'usly'be evaporate from the outer surfaces. As a result, the surface of lumber treated according to this invention remains relatively moist while drying proceeds, water inside the wood travels to the outside, thus drying from the inside out rather than from the outside in, and the surface strains and stresses ordinarily present are reduced to an extent that no appreciable checking or honeycombing occurs. Lumber treated according to this invention exhibits no istics such'as corrosion ofor metallic parts with which it comes in When wood is dipped with urea solutions, saturated "or unsaturated, near room temperature,

wood working tools the amount of urea absorbed on the wood is seasoned wood may be stored, however, and con-Q j amount at approximately 20 (3.).

when the temperature or the wood is at least 5 to 15 C. below .the temperature of the. saturated tion, however, the original water content of wood roughly proportional to the concentration ofurea in the dipping solution. That is also true for under-saturated urea solutions at temperatures above atmospheric where concentration is not greater than about 50% (the saturation However,

urea solution, the amount of urea absorbed on the wood surface is greatly'increased over what.

would be expected. The action of urea solutions 'would indicate that hot saturated water solu tions of many other materials which are more drawn to and' deleterious character'- contact. I

sohible at temperatures above atmospheric than at atmospheric pressure would behave in the same manner. However, testing of a number of such materials which would be expected to act considerations, the pounds of chemical absorbed per 1000 board feet of a given cross section per weight per cent. of chemical in the dipping solution should be roughly constant for all materials and at all temperatures.

Experimental evidence shows, however, that for less than saturated solutions, variation from the average for the above ratio is about plus or minus 32%. Experimental results on saturated solutions of the same substances fall in line with the results on less than saturated solutions except for urea. Absorption of urea from saturated solution at 60' C. was 730% greater than would be expected from its absorption at 20 C. In contrast increase in absorption for the other salts showed 12% for sodium chloride and 19% for potassium formate. These generalities are specifically set forth in the following Tables 1 and 2. a

In carrying out the experiments recorded in Tables 1 and 2, green oak blocks 1" x x 10,". at ordinary temperature (25 C.) were immersed for 5 seconds in a tank of the indicated chemical solution at 20, 40 and 60 C. as indicated in the tables. The blocks were then removed from the solutions in a horizontal position, allowed to drain 5 seconds at an angle of 30 and then placed horizontally to finish draining. The weight of each block was determined after 5 minutes and the increase in weight taken as the amount of solution absorbed.

TABLI 1 Absorption of chemical solutions on oak Conditions Percent complete set'n. of 7 chemical in solution 90 00 90 100 100 100 '6'. C. C. "0. C. C'. Temperature oi solution 20 40 60 20 40 I 60 Lbs chemical absorbed 1000 board Chemical set of 2" x 1 2 sodium chloride s 7 s o e 10 rote-tum iormete..- 36 4c 30 45 48 57 Urea 11 22 20 34 :30

Conditions {Percent eat'n. oi chemical in solution. 00 00 00 100 100 100 C. 0. 0. 6'. 0. C. 'lempenturein eolutiom.-- 20 i0 60 20 4o 00 Wt. ercent chemical in di ing Chum! p solution pp TABLE 2 Absorption of chemical solutions in oak From the above tables and considering the extensive experimental work which we have carried on in treatment of wood according to the process of this invention it appears that the magnitude of the urea deposition and absorption effect is approximately directly related to the temperature difference betweenthe wood and the solution and that this process is not greatly affected by the moisture content of the wood.

Various changes may be made in the preferred embodiments and details of this invention without departing therefrom or sacrificing the advantages thereof.

We claim:

1. In a process for seasoning moisture-containing wood, the step which comprises bringing the outer surface of such wood into contact with a saturated urea solution, the wood being at a temperature at least 5 0. below that of the saturated urea solution. I

2. In a process for seasoning moisture-eontaining wood, the step which comprises bringing the outer surface of such wood into contact with a saturated urea solution, the wood being at a temperature 5-15" 0. below that of the urea solution. I

3. In a process forseasoning moisture-containing wood the step which comprises bringing the outer surface of such wood into contact for 5 to 30 seconds with a saturated urea solution, the wood being at a temperature 5 to 15 C. below that of the urea solution.

4. In a process for seasoning moisture-containing wood, the step which comprises bringing the outer surface of such wood into contact with a saturated urea solution, the wood being at a temperature below that of the saturated urea solution, and thereafter drying the treated wood.

5. In a process for seasoning moisture-containing wood. the step which comprises bringing the outer surface of such wood into contact with -a saturated ureasolution, the wood being at a 

